1. Field of the Invention
The invention relates to an optical connector used to a connection of, for example, an optical fiber for optical communication and a method for assembling same.
2. Discussion of the Background Art
Conventionally, to connect an optical connector, although it is most popular to butt optical fibers against each other and to execute a physical contact connection, in the case, a degree of flatness of an end surface of an optical fiber becomes important. Thus, in a conventional site-assembly-type optical connector, as shown in FIG. 41, a built-in fiber 3 having a polished end surface is disposed in a connector main body 2 into which an optical fiber 1 for line is to be inserted, and the built-in fiber 3 is held by a ferrule 4 as well as the optical fiber 1 for line is connected to the built-in fiber 3 by a mechanical splice by an index matching oil 5. At the time, to accurately align a center of the optical fiber 1 to a center of the built-in fiber 3, a coating 1b of an extreme end of a bare fiber 1a of the optical fiber 1 is removed and the alignment is executed in a state of the bare fiber 1a (refer to, for example, Non-patent Document 1).
A fiber guide 6 for guiding the optical fiber 1 to a connecting portion to the built-in fiber 3 is formed of a groove or a hole into which the optical fiber 1 can be inserted. Accordingly, when a space in which the optical fiber 1 may be buckled exists inside of the optical connector or on a rear end side of the connector, an insertion force equal to or more than an insertion force determined by a size of the space cannot be generated to the optical fiber 1. It is known that when the insertion force is represented by P[N], the insertion force P is determined by a length L[m] of a buckling space (between a fiber holder 7 for holding the optical fiber and the fiber guide 6) (refer to FIGS. 43A and 43B) and shown by the following expression.P=4π2EI/L2  (1)
Here, E represents an elastic coefficient of glass, and I represents a section secondary moment (refer to, for example, Non-patent Document 2). When a force equal to or more than the insertion force is applied in an axial direction of an optical fiber, the optical fiber 1 is buckled in the buckling space and cannot be further inserted. For example, as shown in FIG. 42, when the optical fiber 1 is caught in the fiber guide 6 by foreign substances A such as dusts and a force generated by the caught optical fiber 1 exceeds the insertion force determined by the size of the buckling space, even if it is intended to forcibly push a rear end of the optical fiber 1 into the connector, the optical fiber 1 is buckled in the buckling space and cannot be further inserted into the connector.
In contrast, as a method of removing a coating of an optical fiber, there is a method of using blades 8 having an inner diameter of 175 μm and divided to two portions as shown in, for example, FIG. 45A, holding the optical fiber 1 between the blades 8 from both the sides as shown in FIG. 45B, and removing the coating 1b of the bare fiber 1a by extracting the optical fiber 1 as shown in FIG. 45C (refer to, for example, Non-patent Document 3).
Further, to simplify the assembly job of the site-assembly-type connector as described above, there is also known a method of inserting a coated optical fiber into an optical connector and removing the coating of the optical fiber in a connector main body (refer to, for example, Patent Document 1). In the optical connector, the coating 1b can be exfoliated in the connector by disposing a coating removing section 4b having an insertion port 4a with an inner diameter of 175 μm in the ferrule 4 as shown in FIG. 46A and pushing the optical fiber 1 against an end surface of the coating removing section 4b as shown in FIG. 46B.
In contrast, as a technology for reducing a cost by reducing a number of parts by configuring a site-assembly-type optical connector without using a built-in fiber, there is known also a technology of realizing a physical contact connection by grinding off a corner portion of a cut-off end surface of a line fiber and composing a portion in contact with a confronting fiber of only a flat portion at a center of an end surface (refer to, for example, Non-patent Document 4). In the case, although the fiber is inserted into the connector after an extreme end of the optical fiber is processed, to simplify the assembly job of the site-assembly-type connector as described above, it is also possible to execute a fiber surface preparation in the connector in an assembly process making use of an insertion force of the optical fiber to the connector.    Patent Document 1: Japanese Patent Application Laid-Open No. 2008-292708